Array substrate for in-plane switching mode liquid crystal display device

ABSTRACT

An array substrate for use in an in-plane switching liquid crystal display device includes a plurality of gate lines disposed in a first direction on a substrate; a plurality of data lines disposed in a second direction aslant the gate lines, wherein the gate and data lines have rounded portions and pairs of the gate and data lines define circular pixel regions; a common line disposed in the first direction between the pair of the gate lines; a circular common electrode connected to the common line; a thin film transistor disposed near each crossing of the gate and data lines; and a circular pixel electrode disposed in the circular pixel region, connected to the thin film transistor, and spaced apart from the circular common electrode.

This application is a Divisional of application Ser. No. 10/825,433filed Apr. 16, 2004 now U.S. Pat. No. 7,002,656, which is herebyincorporated by reference as if fully set forth herein. This applicationclaims the benefit of Korean Patent Application No. 2003-0090414, filedon Dec. 11, 2003, which is hereby incorporated by reference as if fullyset forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid crystal display devices. Moreparticularly it relates to liquid crystal display devices implentingin-plane switching (IPS) where an electric field to be applied to liquidcrystals is generated in a plane parallel to a substrate.

2. Discussion of the Related Art

A liquid crystal display device uses the optical anisotropy andpolarization properties of liquid crystal molecules to produce an image.Liquid crystal molecules have a definite orientational alignment as aresult of their long, thin shapes. That alignment direction can becontrolled by an applied electric field. In other words, as an appliedelectric field changes, so does the alignment of the liquid crystalmolecules. Due to the optical anisotropy, the refraction of incidentlight depends on the alignment direction of the liquid crystalmolecules. Thus, by properly controlling an applied electric field, adesired light image can be produced.

Of the different types of known liquid crystal displays (LCDs), activematrix LCDs (AM-LCDs), which have thin film transistors (TFTs) and pixelelectrodes arranged in a matrix form, are the subject of significantresearch and development because of their high resolution andsuperiority in displaying moving images.

LCD devices have wide application in office automation (OA) equipmentand video units because they are light, thin and have low powerconsumption characteristics. The typical liquid crystal display panelhas an upper substrate, a lower substrate and a liquid crystal layerinterposed there between. The upper substrate, commonly referred to as acolor filter substrate, usually includes a common electrode and colorfilters. The lower substrate, commonly referred to as an arraysubstrate, includes switching elements, such as thin film transistorsand pixel electrodes.

As previously described, LCD device operation is based on the principlethat the alignment direction of the liquid crystal molecules isdependent upon an electric field applied between the common electrodeand the pixel electrode. Thus, the alignment direction of the liquidcrystal molecules is controlled by the application of an electric fieldto the liquid crystal layer. When the alignment direction of the liquidcrystal molecules is properly adjusted, incident light is refractedalong the alignment direction to display image data. The liquid crystalmolecules function as an optical modulation element having variableoptical characteristics that depend upon polarity of the appliedvoltage.

In a conventional LCD device, since the pixel and common electrodes arepositioned on the lower and upper substrates, respectively, the electricfield induced between them is perpendicular to the lower and uppersubstrates. However, the conventional LCD devices having thelongitudinal electric field have a drawback in that they have a verynarrow viewing angle. In order to solve the problem of narrow viewingangle, in-plane switching liquid crystal display (IPS-LCD) devices havebeen proposed. The IPS-LCD devices typically include a lower substratewhere a pixel electrode and a common electrode are disposed, an uppersubstrate having no electrode, and a liquid crystal interposed betweenthe upper and lower substrates. A detailed explanation about operationmodes of a typical IPS-LCD panel will be provided referring to FIG. 1.

FIG. 1 is a schematic cross-sectional view illustrating a concept of arelated art IPS-LCD panel. As shown in FIG. 1, upper and lowersubstrates 10 and 20 are spaced apart from each other, and a liquidcrystal layer 30 is interposed there between. The upper and lowersubstrates 10 and 20 are often referred to as an array substrate and acolor filter substrate, respectively. On the lower substrate 20 are acommon electrode 22 and a pixel electrode 24. The common and pixelelectrodes 22 and 24 are aligned parallel to each other. On a surface ofthe upper substrate 10, a color filter layer (not shown) is commonlypositioned in a position between the pixel electrode 24 and the commonelectrode 22 of the lower substrate 20. A voltage applied to the commonand pixel electrodes 22 and 24 produces an electric field 26 through theliquid crystal 32. The liquid crystal 32 has a positive dielectricanisotropy, and thus it aligns parallel to the electric field 26.

Now the description will illustrate the operation of a related artIPS-LCD device. When no electric field is produced by the common andpixel electrodes 22 and 24, i.e., the off state, the longitudinal axesof the liquid crystal (LC) molecules 32 are parallel and form a definiteangle with the common and pixel electrodes 22 and 24. For example, thelongitudinal axes of the LC molecules 32 are arranged parallel with boththe common:and pixel electrodes 22 and 24.

On the contrary, when a voltage is applied to the common and pixelelectrodes 22 and 24, i.e., the on state, an in-plane electric field 26that is parallel to the surface of the lower substrate 20 is producedbecause the common and pixel electrodes 22 and 24 are on the lowersubstrate 20. Accordingly, the LC molecules 32 are re-arranged to bringtheir longitudinal axes into coincidence with the electric field 26.

Therefore, the result is a wide viewing angle that ranges from about 80to 85 degrees in up-and-down and left-and-right sides from a linevertical to the IPS-LCD panel, for example.

FIG. 2 is a plan view illustrating one pixel of an array substrateaccording to a related art IPS-LCD device. As shown, gate lines 40 aretransversely arranged and data lines 42 are disposed substantiallyperpendicular to the gate lines 40. A common line 50 is alsotransversely arranged parallel with the gate line 40 and is spaced apartfrom the gate line 40. The gate line 40, the common line 50 and a pairof the data lines 42 define a pixel region P on the array substrate. Athin film transistor (TFT) is disposed a corner of the pixel region Pnear the crossing of the gate and data lines 40 and 42.

In each one pixel P, three common electrodes 44 extend perpendicularlyfrom the common line 50, and two of the common electrodes 44 aredisposed next to the data lines 42, respectively. A pixel connectingline 48 is disposed next to the gate line 40 with being parallel withthe gate line 40, and is electrically connected to the TFT T. Pixelelectrodes 46 extend perpendicularly from the pixel connecting line 48toward the common line 50. Each of the pixel electrodes 46 is disposedbetween two of the common electrodes 44 parallel with the data line 42.Each of areas “I” between the respective common electrodes 44 and therespective pixel electrodes 46 is defined as a block where the liquidcrystal molecules are rearranged by the electric fields generatedbetween the common and pixel electrodes 44 and 46. In FIG. 2, there arefour blocks in one pixel.

As shown in FIG. 2, the IPS-LCD device according to the related artrearranges and operates the liquid crystal molecules using the electricfield generated parallel with the array substrate. Thus, it can providea wider viewing angle than the LCD device forming the electric fieldperpendicular to the array substrate. Some further modifications havebeen developed in the IPS-LCD device in order to further increase theviewing angle.

FIG. 3 is a plan view of an array substrate for use in an IPS-LCD devicehaving multiple domains according to another related art. With referenceto FIG. 3, some of detailed explanations, especially previouslyexplained with reference to FIG. 2, will be omitted in order to preventduplicate explanations.

In FIG. 3, a pixel connecting line 58 is disposed over a common line 60.Common and pixel electrodes 54 and 56 are elongated from the common andpixel connecting lines 60 and 58, respectively, in an up-and-downdirection. Both the common and pixel electrodes 54 and 56 have a zigzagshape with plural bent portions, and they are parallel to each other andarranged alternately. The zigzag shape defines the multidomains in thepixel regions which are symmetrical to the bent portions of the commonand pixel electrodes 54 and 56. These zigzag shaped structures and themultidomains improve the viewing angle further that the straight shapeof FIG. 2.

Moreover in FIG. 3 the pixel connecting line 58 overlaps the common line60 so that an overlapped area becomes a storage capacitor CST. Namely,the pixel connecting line 58 acts as one electrode of the storagecapacitor CST, while the overlapped portion of the common line 60 actsas the other electrode of the storage capacitor CST. One of the pixelelectrodes 56 is connected to a drain electrode 62 so that all of thepixel electrodes 56 can electrically communicate with the TFT T.

However, the IPS-LCD device having the above-mentioned multidomains hasa problem in that colors shift depending on the viewing angles, due tothe liquid crystal molecules have long and thin shapes.

FIG. 4 is a graph illustrating viewing angle properties of the IPS-LCDdevice having the zigzag structure of FIG. 3. The IPS-LCD device havingthe zigzag-shaped common and pixel electrodes can have the improvedviewing angles in directions of ±90 and ±180 degrees, i.e., inright-and-left and up-and-down directions, as illustrated by references“IVa” and “IVb” in FIG. 4. However, the viewing angles are degraded indirections of ±45 and ±135 degrees, i.e., in diagonal directions, asillustrated by references “IVc” and “IVd” in FIG. 4. Furthermore, colorshift also occurs depending on the viewing angles or directions.

When the voltages applied to the electrodes generate the electric fieldsbetween the common and pixel electrodes, the liquid crystal moleculesrotate about degrees in accordance with the electric fields. Grayinversion occurs due to the rotation of the liquid crystal molecules. Inparticular, when the IPS-LCD is operated in gray mode, the IPS-LCDproduces yellowish color in 45(+45) degrees declination with respect tothe liquid crystal polarization because of the optical anisotropyproperties of liquid crystal molecules. And the IPS-LCD also producesbluish color in 135(−45) degrees declination with respect to the liquidcrystal polarization because of the optical anisotropy properties of theliquid crystal molecules.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an array substrate foran IPS-LCD device that substantially obviates one or more of theproblems due to limitations and disadvantages of the related art.

An advantage of the present invention is to provide an array substratefor use in an IPS-LCD device, which increases a viewing angle andprevents a color sift.

Another advantage of the present invention is to provide an arraysubstrate for use in an IPS-LCD device, which maintains uniformdirection of liquid crystal molecules in all directions.

Another advantage of the present invention is to provide an arraysubstrate for use in an IPS-LCD device, which increases an aperture areain a pixel region.

Additional features and advantages of the invention will be set forth inthe description which follows and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages, an embodiment in accordance withthe principles of the present invention provides an array substrate foruse in an in-plane switching liquid crystal display device. The arraysubstrate includes a plurality of gate lines disposed in a firstdirection on a substrate; a plurality of data lines disposed in a seconddirection aslant the gate lines, wherein the gate and data lines haverounded portions and pairs of the gate and data lines define circularpixel regions; a common line disposed in the first direction between thepair of the gate lines; a circular common electrode connected to thecommon line; a thin film transistor disposed near each crossing of thegate and data lines; and a circular pixel electrode disposed in thecircular pixel region, connected to the thin film transistor, and spacedapart from the circular common electrode.

In another aspect, an array substrate for use in an in-plane switchingliquid crystal display device includes a plurality of gate linesdisposed in a first direction on a substrate; a plurality of data linesdisposed in a second direction perpendicular to the gate lines, whereinthe gate and data lines have a straight line shape and pairs of the gateand data lines define a rectangular pixel regions; a circular commonelectrode disposed in each rectangular pixel region; a common linedisposed to the first direction, the common line connecting the circularcommon electrode to the neighboring circular common electrode disposedin the neighboring rectangular pixel region; a circular pixel electrodedisposed inside the circular common electrode with being spaced apartfrom the circular common electrode; a thin film transistor disposed neara crossing of the gate and data lines in the rectangular pixel region;and a pixel connecting line connecting the circular pixel electrode tothe thin film transistor.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate an embodiment of the presentinvention and together with the description serve to explain theprinciples of that invention.

In the drawings:

FIG. 1 is a schematic cross-sectional view illustrating a concept of arelated art IPS-LCD panel;

FIG. 2 is a plan view illustrating one pixel of an array substrateaccording to a related art IPS-LCD device;

FIG. 3 is a plan view illustrating an array substrate for use in anIPS-LCD device having multiple domains according to another related art;

FIG. 4 is a graph illustrating a viewing angle of the IPS-LCD devicehaving the zigzag structure of FIG. 3;

FIG. 5 is a plan view illustrating an array substrate for use in anIPS-LCD device according a first embodiment of the present invention;

FIGS. 6A and 6B are conceptual illustrations illustrating an exemplarypixel arrangement of the IPS-LCD device having circular common and pixelelectrodes according to the present invention; and

FIG. 7 is a plan view illustrating an array substrate for use in anIPS-LCD device according to a second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to an illustrated embodiment of thepresent invention, examples of which are shown in the accompanyingdrawings. Wherever possible, similar reference numbers will be usedthroughout the drawings to refer to the same or similar parts.

FIG. 5 is a plan view illustrating an array substrate for use in anIPS-LCD device according to a first exemplary embodiment of the presentinvention. In the present invention, the common and pixel electrodeshave a substantially circular shape.

As shown in FIG. 5, gate lines 112 are transversely arranged and datalines 128 are disposed substantially perpendicular to the gate lines112. Pairs of gate and data lines 112 and 128 define regions P on thearray substrate. A thin film transistor (TFT) T is disposed near eachcrossing of the gate and data lines 112 and 128 such that each pixel Pincludes one TFT T. Namely, each of the pixels P has the TFT at a bottomleft corner thereof. The gate and data lines 112 and 128 act as bordersof neighboring pixels P.

In the pixel region, a substantially circular common electrode 120having a substantially circular band shape is disposed. The circularcommon electrode 120 in one pixel P is connected to the neighboringcircular common electrode disposed in the neighboring pixel. Namely, acommon line 114 substantially perpendicularly crosses the data line 128and connects the neighboring circular common electrodes 120. A circularpixel electrode 138 is disposed inside the circular common electrode 120and spaced apart from the circular common electrode 120. The pixelelectrode 138 also has a circular band shape and is connected to the TFTT through a pixel connecting line 140. Namely, the pixel connecting line140 extends from a side of the circular pixel electrode 138 and contactsthe TFT to transfer the electric signals from the TFT T to the pixelelectrode 138.

An aperture area defined between the circular common and pixelelectrodes 120 and 138 also has a circular band shape such that theliquid crystals located in such aperture area have the liquid crystaldirectors that are constant in all directions. Therefore, a color shiftis prevented and an image quality increases in the IPS-LCD device.Additionally, although FIG. 5 shows only one common electrode and onepixel electrode in the pixel region P, plural common and pixelelectrodes are possible so as to form multi domains within one pixelregion P.

The array substrate depicted in FIG. 5 shows the gate and data lines 112and 128 shaped like straight lines, and each of the pixel regions Pdefined by the gate and data lines 112 and 128 is shaped like arectangle, for example, as being a box type. And circular common andpixel electrodes 120 and 138 are formed inside the rectangular pixelregion P. Therefore, dummy areas DA, which do not function as theaperture area, exist in the pixel region P because of the profiledifferences between the rectangular pixel region P and the circularcommon and pixel electrodes 120 and 138. Those dummy areas DA cause thedecrease of the aperture ration in the IPS-LCD device. To overcome thisdisadvantage, some modifications are developed as illustrated in FIG. 7.

FIGS. 6A and 6B are conceptual illustrations showing exemplary pixelarrangements of the IPS-LCD device having circular common and pixelelectrodes according to the present invention.

In FIG. 6A, each pixel region P has a rectangular shape and the circularcommon and pixel electrodes CE are disposed inside the rectangular pixelregion P. Furthermore, if lines are drawn to connect the centers of thecircular common and pixel electrodes CE, four pixel regions P form arectangle A. This configuration can be referred to as a stripe structurebecause the pixel regions P are disposed parallel side-by-side alongsidevertical or horizontal lines.

FIG. 6B shows a pixel arrangement modified from FIG. 6A. As compared toFIG. 6A, the pixel region of FIG. 6B is not shaped like a rectangle, butthe common and pixel electrodes CE have a substantially circular shapeand are disposed in the center of the pixel regions as like those ofFIG. 6A. If lines are drawn to connect the centers of neighboring threepixel regions, a triangle B is accomplished. Further, if lines are drawnto connect the centers of neighboring four pixel regions, aparallelogram C is accomplished. This configuration forming the triangleor the parallelogram can be referred to as a delta structure or aparallelogram structure because of the above-mentioned profiles. Thedelta structure of FIG. 6B can reduce the intervals among the circularcommon and pixel electrodes CE, thereby reducing the dummy area as muchas a residual area R in comparison with the stripe structure depicted inFIG. 6A. This means that the delta structure increases the apertureratio relative to the stripe structure.

FIG. 7 is a plan view illustrating an array substrate for use in anIPS-LCD device according to a second exemplary embodiment of the presentinvention. In this second embodiment, the aforementioned delta structureis utilized in order to minimize the dummy area that does not functionto display images.

Common lines 214 are transversely disposed on a substrate with beingspaced apart from each other. Gate lines 212 are disposed in a rowdirection on the substrate while running from left to right in thecontext of the figure alongside the common lines 214. Data lines 228 aredisposed in a column direction aslant the gate line 212. Pairs of thegate and data lines 212 and 228 define a pixel regions P. The gate anddata lines 212 and 228 are curved in each pixel region P such that theyare circuitous around the pixel regions P. Namely, the pixel regions Pof the second embodiment are shaped like a circle unlike the firstembodiment illustrated in FIG. 5 because the gate and data lines 212 and228 are formed to be rounded around the pixel regions P.

Near each crossing of the gate and data lines 212 and 228, a thin filmtransistor (TFT) T is disposed. The TFT T includes a source electrode250 and a drain electrode 252. The source electrode 250 extends from thedata line 228 over a portion of the gate line 212. The drain electrode252 is spaced apart from the source electrode 250, overlaps a portion tothe gate line 212, and extends into the pixel region P.

Within each pixel region P, a circular common electrode 220 and acircular pixel electrode 238 are disposed. The circular common electrode220 includes a first circular common electrode pattern 220 a and asecond circular common electrode pattern 220 b both of which extend fromand are connected to the common line 214. The common line 214 passesalong a diameter of the first and second circular common electrodepatterns 220 a and 220 b such that the common line 214 divides the firstand second circular common electrode patterns 220 a and 220 b into twosemicircular portions, respectively. The first circular common electrodepattern 220 a is larger than the second circular common electrodepattern 220 b such that the second circular common electrode pattern 220b is disposed inside the first circular common electrode pattern 220 a.Meanwhile, the first circular common electrode pattern 220 a has anopening in order to prevent the intersection with the drain electrode252.

The circular pixel electrode 238 is comprised of first and secondcircular pixel electrode patterns 238 a and 238 b. The first circularpixel electrode pattern 238 a is shaped like a circular band and isdisposed between the first and second circular common electrode patterns220 a and 220 b. The second circular pixel electrode pattern 238 b isdisposed inside the second circular common electrode pattern 220 b. Apixel connecting line 241 connects the first and second circular pixelelectrode patterns 238 a and 238 b, and extends over a portion of thefirst circular common electrode pattern 220 a.

Meanwhile, a capacitor electrode 221 is disposed over a portion of thefirst circular common electrode pattern 220 a and is connected to thepixel connecting line 241. The capacitor electrode 221 and theoverlapped portion of the first circular common electrode pattern 220 aconstitute a storage capacitor Cst with an interposed dielectric layer(not shown). The capacitor electrode 221 acts as a first electrode ofthe storage capacitor Cst, and the overlapped portion of the firstcircular common electrode pattern 220 a acts as a second electrode ofthe storage capacitor Cst. Although FIG. 7 shows that the capacitorelectrode 221 is disposed over the first circular common electrodepattern 220 a, the capacitor electrode 221 maybe disposed over theprevious gate line 212 disposed for the previous pixel regions P. Thefirst circular pixel electrode pattern 238 a is connected to the drainelectrode 252 such that it receives data signals from the data line 228via the TFT T.

In the pixel region P shown in FIG. 7, the aperture areas between theelectrode patterns are shaped like circles because the common and pixelelectrode patterns 220 a, 220 b, 228 a and 228 b have the circularshapes. Furthermore, since the gate and data lines 212 and 228 havefound portions corresponding to the circular common and pixel electrodes220 and 228, the pixel regions P also have the circular shape.

According to the second embodiment of FIG. 7, the pixel regions P havethe formation of the delta structure or the parallelogram structure asillustrated with reference to FIG. 6B. Namely, the pixel regions aredistributed parallel from left to right in the context of the figure,but obliquely from top and bottom in the context of the figure. Whendrawing the lines to connect the centers of the three pixel regions P,the lines form like a letter delta (Δ), i.e., the delta structure. Also,when drawing the lines to connect the centers of the four pixel regionsP, the lines form a parallelogram, hence the parallelogram structure.The circular pixel regions and the delta or parallelogram structure canreduce the dummy area as compared to with the stripe structure of FIG.5, because the circular pixel regions P are closely located to eachother. Therefore, the aperture ratio can increase.

Further embodiments are contemplated by the present invention in whichpixels, pixel electrodes, and common electrodes have a polygonal shaperather than a circular band shape. For example, pixels may have theshape of polygons having five or more sides. It is understood that asthe number of sides in the regular or equilateral polygon increases, thepolygonal shape approaches a substantially circular shape.

Accordingly in the present invention, it is possible to obtain a widerviewing angle due to the circular-common and pixel electrodes. The colorshift is also prevented, and the contrast and resolution of the IPS-LCDincreases due to the fact that the liquid crystal directors are alluniform in all directions. Furthermore, since the dummy area is reducedwhen the pixel regions are rounded and the delta or parallelogramstructure is utilized, the aperture ratio increases.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the array substrate of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

1. An array substrate for use in an in-plane switching liquid crystal display device, comprising: a plurality of gate lines disposed in a first direction on a substrate; a plurality of data lines disposed in a second direction perpendicular to the gate lines, wherein the gate and data lines have a straight line shape and pairs of the gate and data lines define a rectangular pixel regions; a circular common electrode disposed in each rectangular pixel region; a common line disposed to the first direction, the common line connecting the circular common electrode to the neighboring circular common electrode disposed in the neighboring rectangular pixel region; a circular pixel electrode disposed inside the circular common electrode with being spaced apart from the circular common electrode; a thin film transistor disposed near a crossing of the gate and data lines in the rectangular pixel region; and a pixel connecting line connecting the circular pixel electrode to the thin film transistor, wherein the thin film transistor is disposed at a corner of the pixel region and wherein the distance between the common line and two adjacent gate lines is substantially the same.
 2. The array substrate of claim 1, wherein the circular pixel electrode has a circular band shape.
 3. The array substrate of claim 1, wherein the circular common electrode has an open corresponding in position to the thin film transistor, and the pixel connecting line passes through the open.
 4. The array substrate of claim 1, wherein the pixel connecting line does not cross the rectangular pixel region but cross over the gate line.
 5. The array substrate of claim 1, wherein the circular common and pixel electrodes constitute a circular aperture area.
 6. The array substrate of claim 1, wherein the pixel regions have a formation of straight structure where the pixel regions are distributed parallel both from left to right and from top and bottom.
 7. The liquid crystal display device of claim 1, wherein first and second adjacent pixels in a first row and a third pixel adjacent to said first and second pixels in a second row form a delta structure, each of three vertices of the delta structure being a center of the first, second and third pixels, respectively. 